001/*
002 * Copyright (c) 2015-2020, Oracle and/or its affiliates. All rights reserved.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.tribuo.math.util;
018
019import java.io.Serializable;
020
021/**
022 * Normalizes the exponential values of the input array. Used when the input is in log space.
023 */
024public class ExpNormalizer implements VectorNormalizer, Serializable {
025    private static final long serialVersionUID = 1L;
026
027    @Override
028    public double[] normalize(double[] input) {
029        double[] output = new double[input.length];
030        double max = -Double.MAX_VALUE;
031        for (int i = 0; i < input.length; i++) {
032            if (max < input[i]) {
033                max = input[i];
034            }
035        }
036        double sum = 0.0;
037        for (int i = 0; i < input.length; i++) {
038            output[i] = Math.exp(input[i] - max);
039            sum += output[i];
040        }
041        for (int i = 0; i < output.length; i++) {
042            output[i] /= sum;
043        }
044        return output;
045    }
046
047}